Many semiconductor devices, which are sometimes referred to as integrated circuit chips, are enclosed in a plastic, ceramic or similar protective material as part of the finished semiconductor package. Typically, a series of conductive leads project out from the protective material. The leads connect the chip to external circuits on a printed circuit board. The conductive leads are plugged in or soldered to the printed circuit board. Many different types of packages are commonly used in the manufacture of semiconductor devices. For example, single in line packages (SIPs) have a single row of conductive leads. Dual in line packages (DIPs) have two rows of leads. SIPs and DIPs are mounted on a printed circuit board by inserting the leads through holes in the board. By contrast, the leads of surface mounted packages are soldered to the printed circuit board. Small outline J lead packages (SOJs) with J shaped leads and thin small outlined packages (TSOPs) with gull wing shaped leads are examples of surface mounted packages.
At the end of the semiconductor manufacturing process, and after the chip has been enclosed in protective material, the conductive leads are trimmed and formed into the desired shape. Because molded plastic packages are the most common, the trim and form operations used in the manufacture of molded plastic packages will be described to provide further background for the invention. The individual semiconductor chips are attached to a metal lead frame. The number of frames on a strip depends on the size of the package, the spacing of the chips and the length of the strip. The chips on each lead frame strip are processed together. Thus, it is desirable to increase the number of chips on a leadframe strip to increase the capacity of the processing equipment. After the chips are encapsulated in plastic, the lead frame strip is conveyed through a series of presses in which excess plastic is cut from the package (called deflash), the resin dams are cut (called dedambar--the resin dams are bars in each lead frame that prevent the molten plastic from flowing out along the protruding conductive leads), and then the leads are cut from the lead frame (called leadshear). The leads are usually bent into the desired shape just before or after the leadshear.
The package is trimmed and the leads formed by moving the lead frame strips through a lead forming tool called a press, or a series of presses. Each press includes a die and a punch or a series of dies and punches. As a punch is pressed against a die (or, in some cases, the die is raised up against the punch), the semiconductor package is deflashed, dedambarred, leadsheared and the leads formed in the lead bending steps. During lead bending, shear forces tend to weaken or damage the leads. Also, the punch tends to slide across and scrape the surface of the leads. Tin, lead, palladium and other surface plating materials are often used on the conductive leads to improve the physical and electrical characteristics of the leads. Some of the plating material may be scraped off during lead bending. In addition to adversely effecting the characteristics of the lead, this plating material collects on the die and punch. As a result, the punch and die must be cleaned or replaced periodically.
In an effort to minimize damage to the leads and to reduce maintenance on the punch and die, some lead forming tools use a "pivot punch" instead of a straight punch. A pivot punch pivots into the leads as it is pressed into the die to reduce shear forces on and minimize surface damage to the leads. In a conventional pivot punch, the punch rotates on a pin. Although conventional pivot punches can be effective to reduce shear forces and minimize surface damage, they are not well suited to closely spaced chips on the lead frame strips. The "pitch" of a lead frame strip reflects the spacing of the lead frames and corresponds to the spacing of the semiconductor chips on each strip. For example, in a 0.6 inch pitch lead frame strip, each chip is spaced 0.6 inches from the adjacent chips. It would be difficult and expensive to fabricate and assemble a conventional pivot punch that would work well in this high pitch lead frame strip. The conventional pivot punch components would, in any event, be very fragile and unlikely to function effectively in production.